The Nautical Magazine: A Journal of Papers on Subjects Connected with ..., 10권

could exist for entertaining such an assumption. When Mr. Sturgeon shall have adduced some instances of the effect in question, any one accredited fact, I may then perhaps be led “to make known to the Admiralty that such is the case ;” until this however be done, he must exeuse me, if I shall not deem it necessary to trouble their lordships.

The following table, containing some remarkable instances in which discharges of lightning traversed lightning conductors, in ships of her Majesty's Navy, without producing any effect whatever on the compasses, is quite sufficient to shew the fallacy of Mr. Sturgeon's vaunted objection.

“Permit me," he says, " to ask you a few questions on this subject. Do you wish me to understand that you, a Fellow of the Royal Society, are totally ignorant of Sir H. Davy's experiments, by which that philosopher first magnetized steel needles, by transmitting electric discharges from a battery of jars through a vicinal conduct ing wire? Do you wish me to understand that you, a Fellow of the Royal Society, with the pretensions of an electro-magnetist, never repeated those beautiful experiments? Do you wish me to understand that you, a Fellow of the Royal Society, who as an inventor of a marine lightning conductor, ought to be a profound electrician, and electro-magnetist, thout you who are pretending to protect the British Navy, and our brave tars from the effects of lightning,—that you, on whose jadgmeat such mighty interests are to be at stake, are entirely ignorant of the laws of electro-magnetism? If you are not entirely ignorant of the magnetic action of electric currents traversing good conductors, how dared you venture to say that it is only in the absence of continunus conductors we find such magnetic effects. If you are not entirely ignorant of such magnetic action, how dared you venture to stain the pages of British science, to insult the dignity of the Royal Society, and above all to deceive the Lords Commissioners of the Admiralty, and the whole British Navy, by propagating such a palpable falsehood? Will you acknowledge that you are ig. norant of the magnetic action of lightning whilst traversing good conductors, or will you have to submit to the degrading position of having wilfully concealed that most important fact, to guard against which, is one of the most essential considerations in the erection of marine lightning conductors?"

Now the charlatanism of this rare ebullition of Mr. Sturgeon's small mind, is " too definite to be easily mis-understood." If it is in fact as applicable to Dr. Wol

The cases of the Druid, Beagle, and Dryad, fitted with my conduca tors, are conclusive on the point in question, and Mr. Sturgeon has no means of getting out of the difficulty except by denying the facts ; this he accordingly does without any scruple, and says in plain terms, that the officers who witnessed these shocks of lightning were not judges of what they saw, notwithstanding they were well acquainted with the effects of lightning on ships.

Thus Lieutenant Sullivan informs us, he was in her Majesty's ship Thetis, when her foremast was struck in pieces by lightning, that he was the officer of the watch, and on deck, when the Beagle having my conductors was struck by lightning, that the shock was still more severe than he experienced in the Thetis, that the mast appeared enveloped in a blaze of fire, and the ship fairly shook under the stroke. Capt. Turner says he was on deck, and saw the lightning fall with a terrible crash, first on the foremast and then on the mizen-mast of the Dryad, at the time of a tornado on the Coast of Africa.

Captain Norcott says, at Rio Janeiro one night, there was awful lightning, which was conducted down the fore and main masts of the Druid,-it was visible, &c.

All this testimony, however, Mr. Sturgeon endeavours to get rid of by a well-known figure of speech, called nonsense. The phenomena he says, did not arise from a dense shock of lightning, but from an electrical wave produced by a near discharge. His ideas of this wavy discharge seem to be sufficiently vague and indeterminate. He says, it is produced by the expansive force of the discharge, and “ this I ought to have known, that it would effect a gold-leaf electrometer, &c.”

This is something quite new,- I was certainly not aware that a goldleaf electrometer would be affected by expansion of the air before; if so, then every time a cannon is fired, the leaves of an electrometer at a short distance from it should diverge. The only effect of an electrical kind, which could be imagined during a discharge of lightning, is a sort of propagation of electrical action through contiguous particles of the air by induction, but which evidently does not arise in consequence of the expansive effect of the explosion.

"I even found,” says Priestly, that the explosion of a battery made erer so near a brass rod, did not so much as disturb its electric fluid, for when I had insulated the rod, and hung a pair of pith balls on the end opposite to that near which the explosion passed, I found the balls were not in the least moved.”

This is quite conclusive of the fallacy of Mr. Sturgeon's wavy discharge, on the supposition of its being produced by the expansive force of an explosion, and directly contradicts his assertion, “ that an electrical wave is produced by artificial discharges."*

It is certainly highly probable that a gold-leaf electrometer involved in an electrified atmosphere, would be affected by electrical changes in laston who gave my plan his approval, and for whom Mr. Sturgeon professes to have a “great veneration," as to me it is certainly a very novel form of philosophical reasoning.

* It is quite clear that either Dr. Priestly or Mr. Sturgeon must be wrong, I feel quite assured it is not Dr. Priestly.

that atmosphere induced by discharges of lightning; but we cannot suppose the existence of a discharge under the form of a wave, bearing all the characters of a direct stroke of lightning.

How is it that the evidence of any naval officer is not called in question by Mr. Sturgeon, in any case except in these three cases relating to my conductors ?

Plainly because these cases overturn all he has advanced on the subject.

His conclusion, sec. 207, that because the chronometers did not suffer from electro-magnetic action, therefore, the ship could not be struck by lightning, is clearly taking that for granted, which requires to be proved,-a sort of begging of the question of which the meanest reasoner would be ashamed ;-he had only to push this fallacy a little further, and then he would just as clearly have sbewn that in no case has any ship really been struck by lightning, in which the compasses and chronometers were not affected, notwithstanding that the masts had been shivered to the keelson, or conductors melted by the shock.*

What sort of philosophy is this?

The severe philosophical scrutiny which the late Dr. Wollaston bestowed on every question submitted for his consideration, would lead any oue to infer that the probable electro-magnetic action of lightning conductors had not escaped him, more especially as Sir H. Davy in his account of the electro-magnetic action, actually gives it under the form of a letter, addressed to Dr. Wollaston himself; he states in this letter, that one of tbe experiments arose out of a conversation they had previously held together on the subject.

Now, it happens most unfortunately for Mr. Sturgeon that this occurred, at the very time my system began to be entertained by the Navy Board, and only a short time before, Dr. Wollaston wrote a letter to the Comptroller of the Navy, expressing his full approbation of it.

Mr. Sturgeon will therefore permit me to ask him a few questions on this subject, and which as a reductio ad absurdum, I will proceed to do after his own very refined style, and as nearly as possible in his own words above given. Does he wish us to understand that Dr. Wollaston, a Fellow of the Royal Society, was totally ignorant of Sir H. Davy's experiments, by which that philosopher first magnetized steel needles by the electric discharge? Does he wish us to understand that Dr.

* The presence of a continuous conductor is not essential to the electro-magnetic effect of an electrical discharge.

Davy found that needles became magnetic, when exposed to an electrical explosion passing through the air.

It would be quite impossible to analyze the many unwarrantable assumptions found in Mr. Sturgeon's various publications on this subject.

Thus he supposes that the complicated distribution of copper rods he has proposed as conductors, would neutralize each others action on the compasses, because the discharge would pass equally on both sides; but it is evident, that in no case would the compasses or chronometers be found placed in a spot perfectly neutral to all the surrounding forces, nor does it follow that the passing electricity would be equal on each side of it. The compasses and chronometers are placed a long way behind the mast and rigging, and frequently much nearer on one side of the ship than the other, besides, a compass needle might be right across, or in a transverse position to the rigging on one side, and not on the other, which would make all the difference.

Wollaston, a Fellow of the Royal Society, with the pretensions of an electro-magnetist, never repeated these beautiful experiments ? Does he wish us to understand that Dr. Wollaston, a Fellow of the Royal Society, who as an investigator of a marine lightning conductor, ought to be a profound electrician and electro-magnetist, was entirely ignorant of the laws of electro-magnetism? If he was not ignorant of electro-magnetic action, how dared he to stain the pages of British science? insult the Royal Society, and above all deceive the Lords Commissioners of the Admiralty, and the whole British Navy, by telling the Comptroller of the Navy that “he saw no danger, or insecurity or liability to objection in Mr. Harris's method ? That Mr. Harris appeared to be well acquainted with his subject, and to fairly estimate the powers of the element with which we have to contend."

Will, then, Mr. Sturgeon assert, that Dr. Wollaston was ignorant of electro-magnetic action, or will he put himself in the degrading position of a detractor, (an amiable character he has lately assumed in his remarks on one of the best of men, as well as one of the most powerful philosophers of the present day, Dr. Faraday,*) and tell his readers that Dr. Wollaston wilfully concealed a most important fact,—to guard against which, is one of the most essential considerations in the erection of marine lightning conductors ?

Why Mr. Sturgeon should have made his attack on me a channel for the further publication of his scurrilous remarks on Faraday it would be difficult to say. His assertions that this celebrated philosopher had transplanted his (Mr. Sturgeon's,) discoveries into the philosophical transactions, and made them his own,t have not clearly any bearing on the question now under consideration. His various misrepresentations of Dr. Faraday have not escaped the indignant attention of our continental neighbours.

I shall conclude what I have further to say on the remaining parts of Mr. Sturgeon's memoir in my next communication.

Yours, &c.

W. Snow HARRIK. To the Editor of the Nautical Magazine.

ON THE LONGITUDES OF THE PRINCIPAL MARITIME PointS OF THE

Globe.—By Lieut. Raper, R.N., Sec. R.A.S.

Sect. V. continued from vol. for 1839, p. 758. Since the publication of the preceding paper of this series a communication has been received from Commander Barnett, containing some positions on the lake of Nicaragua, and some chronometric differences between important points which have already been under consideration.

As the arrival of new data during the progress of this discussion, may be expected to occur more or less frequently, it is proper to state here that we shall, on such occasions proceed at once to the consideration of fresh matter, in order to avoid the postponement of necessary corrections. The only evidence of this disturbing the order originally intended, by the introduction of matter of a more recent date than that of the commencement of the discussion itself, will be that some places will have two or more numbers; this however can lead to no inconvenience be. cause the numbers are used merely for reference, and do not necessarily indicate geographical connection.

We have remarked (No. 34) that the diff. long. between Havana and Port Royal was not, as far as our information went, satisfactorily established. Commander Barnett has obtained further measures of the meridian distance between these places.